Approximately 20 minutes from Gastonia (between Charlotte and Gastonia) is the US National Whitewater Center. Parking is $5 but the Whitewater Center has plenty of free and low cost options such as hiking, zip lining, ropes courses, whitewater rafting, rock climbing, mountain biking, etc. You could spend the entire day there! Check out their website for information and Day Pass pricing: https://center.whitewater.org/
Daniel Stowe Botanical Gardens is about 15-20 minutes from Gastonia. Price for general admission is around $15 for general daytime admission to checkout the gardens. Make sure to check their hours on the website: https://dsbg.org/visit/
Uptown Charlotte is about a 30 minute drive from Gastonia.